Loading distribution

The development of finite element methods, since the late 1960s, has made possible the exploration of a wide range of variables relevant to the design of screwed plug closures. Work (126,128—132) on the stress at the toot of the first loaded thread, where most failures occur, and the load distribution along the thread length has led to the conclusions that the load carried by the first three threads decreases considerably as the number of active threads increases to 20, and the load carried by the second thread, is approximately 75% of the load on the first thread, f, and that on the third thread, fj, about 60% of f, that on the first thread, regardless of the number of threads. 

Empirical equations have been proposed (133) which enable a combination of thread and vessel parameters to be chosen to minimise the stresses at the toot of the first three active threads. The load distribution along the thread is sensitive to machining tolerances and temperature differentials (134) and... 

Many institutions have hundreds, or even thousands, of powerful work stations that are idle for much of the day. There is often vastiy more power available in these machines than in any supercomputer center, the only problem being how to harness the power already available. There are network load-distribution tools that allocate individual jobs to unused computers on a network, but this is different from having many computers simultaneously cooperating on the solution of a single problem. 

Spheres, spheroids, and toroids use steel or concrete saddles or are suppoi ted by columns. Some may rest directly on soil. Horizontal cyhndrical tanks should have two rather than multiple saddles to avoid indeterminate load distribution. Small horizontal tanks are sometimes supported by legs. Most tanks must be designed to resist the reactions of the saddles or legs, and they may require reinforcing. Neglect of this can cause collapse. Tanks without stiffeners usually need to make contact with the saddles on at least 2.1 rad (120°) of their circumference. An elevated steel tank may have either a circle of steel columns or a large central steel standpipe. Concrete tanks usually have concrete columns. Tanks are often supported by buildings. 

Loads of welding sets, which have intermittent duty cycles, are mostly single phase, cause low p.f. and stress the generator windings intermittently. Unbalanced loads, such as single phase loads, distributed unevenly cause current unbalance and low p.f. 

Capacity control is more complex in compressor networks where two or more compressors operate in series or parallel. Automatic distribution of the load between compressors is required. The antisurge and load sharing control loops must be coordinated to ensure surge protection while tlie load distribution and energy consumption are optimized. 

Information on load distributions was virtually non-existent until quite recently although much of it is very rudimentary, probably because collecting data is very expensive, the measuring transducers being difficult to install on the test product or prototype (Carter, 1997). It has been cited that at least one prototype is required to make a reliability evaluation (Fajdiga et al., 1996), and this must surely be to understand the loads that could be experienced in service as close as possible. 

Equation 4.34 represents probably one of the most important theories in reliability (Carter, 1986). The number of load applieations defines the useful life of the eompo-nent and is of appropriate eoneern to the designer (Bury, 1974). The number of times a load is applied has an effeet on the failure rate of the equipment due to the faet that the probability of experieneing higher loads from the distribution population has inereased. Eaeh load applieation in sequenee is independent and belongs to the same load distribution and it is assumed that the material suffers no strength... 

Gn L) is often difficult to determine for a given load distribution, but when is large, an approximation is given by the Maximum Extreme Value Type I distribution of the maximum extremes with a scale parameter, 0, and location parameter, v. When the initial loading stress distribution,/(L), is modelled by a Normal, Lognormal, 2-par-ameter Weibull or 3-parameter Weibull distribution, the extremal model parameters can be determined by the equations in Table 4.11. These equations include terms for the number of load applications, n. The extremal model for the loading stress can then be used in the SSI analysis to determine the reliability. 

The calculated loading stress, L, on a component is not only a function of applied load, but also the stress analysis technique used to find the stress, the geometry, and the failure theory used (Ullman, 1992). Using the variance equation, the parameters for the dimensional variation estimates and the applied load distribution, a statistical failure theory can then be formulated to determine the stress distribution, f L). This is then used in the SSI analysis to determine the probability of failure together with material strength distribution f S). 

To determine the stress at any point on the seetion requires that the load be resolved into eomponents parallel to the prineipal axes. Eaeh eomponent will eause bending in the plane of a prineipal axis and the total stress at a given point is the sum of the stress due to the load eomponents eonsidered separately. However, first we must eonsider the nature of the loading distribution and how it is resolved about the prineipal axes. 

Table 19-8 shows a load-distribution program for an 87.5-MW power station of steam turbines and gas turbines. The seleetion of equipment and their loading for the most effieient operation ean be programmed when the effieieney of individual units are monitored. The program... 

Combination of Units of Yieid Efficient Power Load Distribution for Different Demand Loads... 

Bonded-bolted joints have good load distribution and are generally designed so that the bolts take all the load. Then, the bolts would take all the load after the bond breaks (because the bolts do not receive load until the bond slips). The bond provides a change in failure mode and a sizable margin against fatigue failure. 

However, rolls are highly prone to loads induced by the process. In most cases, rolls carry some form of product or a mechanism that, in turn, carries a product. For example, a simple conveyor has rolls that carry a belt, which carries product from one location to another. The primary monitoring parameters for process rolls include bearings, load distribution, and misalignment. 

For the speed and load distributions three superposed normal distributions around three fixed mean values are used, corresponding for the speed to town, country road, and motorway (turnpike or freeway) traffic. A maximum speed fixes the total width of the curve from zero to that maximum. This corresponds to lOtr, where a stands for standard deviation of the three superposed distributions. The three mean values are fixed at 3, 5, and la. Their heights can be varied according to the frequency with which the three distributions occur, their sum has to add up to LA similar distribution is also used to describe the different load conditions with low, medium, and high loads. Figure 26.79 gives an example of such a triple distribution function. 

FIGURE 26.79 Theoretical triple distribution as they are used in a computer simulation for speed and load distributions (height ratios town 0.7, country 0.2, and motorway 0.1). 

The tire constmction influences both cornering and longitudinal slip stiffness. These include the tire carcass, breaker construction, inflation pressure, and tread pattern design. However, since the two stiffness components can be measured, knowledge of the construction details is not necessary. The vehicle geometry influences the tire wear through the air resistance, which it creates, and through the load distribution between front and rear axles. 

Since no data apart from a description of the general use of the tmck (mostly short-distance haulage) and the axle position on which the tires were mounted were available, again reasonable assumptions on maximum accelerations and speeds, as well as load distributions had to be made. They are hsted in Table 26.9 together with the three comparisons. 

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